Current Transformer (CT) – Construction and Working Principle

Uses / Advantages of Current Transformer
Current transformers are used extensively for measuring current and monitoring the operation of the power grid.

Application of different types of Current Transformers
Along with voltage leads, revenue-grade current transformers drive the electrical utility’s watt-hour meter on virtually every building with three-phase service and single-phase services greater than 200 amperes. 
High-voltage current transformers are mounted on porcelain or polymer insulators to isolate them from the ground. 
Current transformers can be mounted on the low voltage or high voltage leads of a power transformer.
Often, multiple CTs are installed as a “stack” for various uses. For example, protection devices and revenue metering may use separate CTs to provide isolation between metering and protection circuits and allows current transformers with different characteristics (accuracy, overload performance) to be used for the devices.
Application of High Voltage Current Transformers
Ideal for installation at metering points due to its very high accuracy.
Excellent frequency response; ideal for monitoring power quality and measuring harmonics.
Suitable for installation in AC and DC filters in converter substations for HVDC projects.
Examples of applications:

1. 
   Protection for high voltage lines and substation.
   
2. 
   Protection for capacitor banks.
   
3. 
   Protection for power transformers.
   
4. 
   Revenue metering.
   

What is Potential Transformer?

A Potential Transformer is also introduced as a voltage step-down device or instrument transformer, or voltage transformers, in which the voltage of a circuit is dropped to a lower voltage for detection. The electromagnetic instrument applied for transforming the greater voltage of the network to the lower voltage is known as a potential transformer. The output of a low voltage network can be sensed with wattmeters or voltmeters. These are able to decrease or increase the voltage ratings of a circuit without a variation in its windings and frequency. The working principle and structure of a potential transformer are the same as the conventional and power transformers.